Argon bubble flow in liquid gallium in external magnetic field

Abstract

This paper presents detailed results of neutron imaging of argon bubble flows in a rectangular liquid gallium vessel with and without the application of external horizontal magnetic field. The developed image processing algorithm is presented and its capability to extract physical information from images of low signal-to-noise ratio is demonstrated. Bubble parameters, velocity components, trajectories and relevant statistics were computed and analysed. A simpler version of the code was applied to the output of computational fluid dynamics simulations that reproduced the experiment. This work serves to further validate the neutron radiography as a suitable method for monitoring gas bubble flow in liquid metals, as well as to outline procedures that might help others to extract data from neutron radiography images with a low signal-to-noise ratio resulting from high frame rate acquisitions required to resolve rapid bubble motion.

Phase boundary dynamics of bubble flow in a thick liquid metal layer under an applied magnetic field

“…Material parameters used in the CFD models and the tools used to solve Eqs. (1)-(5) numerically are found in [37]. Preliminary analysis of our setup, images, and simulations show that one has Fr ∈ [0.2; 0.3], implying that buoyancy is the main driving force, as expected.…”

“…Applied horizontal MF (HMF) was seen to stabilize bubble trajectories, damping lateral velocity and displacement, and resulting in nearly straight ascension paths, as opposed to zigzag motion observed without MF. Image-based velocimetry revealed bubble acceleration in the upper half of the melt container in the presence of MF, while the opposite is seen without applied MF [37]. Hereinafter, we demonstrate that our approach also resolves phase boundary dynamics, not just translational motion.…”

“…The setup ( Fig. 1), a detailed description of which is found in [37], consisted of a 150 × 90 × 30 mm 3 glass container filled with liquid Ga, wherein Ar bubble chain flow was introduced via a submerged copper tube with a constricted nozzle, which ejected bubbles such that they ascended without wall interactions. This was necessary to isolate and study the bubble-bubble interactions and MF effects.…”

“…Neutron images were dark current and flat-field corrected, denoised using the self-snakes type curvature flow filter, then bubble shapes were extracted via double-Otsu morphological binarization and Shen-Castan edge detection with bubble interior and edge restoration subroutines. Bubble shape parameters were derived from best-fit ellipses [37].…”

“…2(a), note that initially the error band of the simulated curve is much narrower. During bubble formation at the horizontally directed (and thus asymmetric) inlet tube [37], the bubble is stretched vertically by the buoyancy forces and laterally due to hydrodynamic gas pressure at the tube opening; then, once the bubble detaches, surface tension forces retract the lagging part of the bubble towards its center of mass, resulting in self-propulsion and rapid initial acceleration responsible for the starting negative φ values. This is illustrated in Fig.…”